Conventionally, radio-controlled timepieces are known that receive standard time and frequency signals, which include time information, and correct the time based on the time information.
There are numerous schemes for configuring the receiver circuit of a radio-controlled timepiece. To receive multiple frequencies, a timepiece uses a heterodyne scheme, where the receiver circuit configuration includes a variable frequency local oscillator and a MIX circuit is known (for example, refer to Patent Documents 1 and 2 below).
Typically, in a heterodyne receiver circuit, a specialized oscillator circuit that maintains high accuracy is used for the reference signal for the local oscillator. However, on top of being costly, such a specialized, high-accuracy oscillator circuit consumes significant power and is large. Therefore, equipping such an oscillator circuit into a system having limited energy and space, such as a radio-controlled timepiece, is difficult.
Thus, in Patent Document 1, a radio-controlled timepiece is disclosed that saves space, is low-cost, and can receive multiple frequencies by employing a heterodyne scheme in configuring the receiver and using, as the reference frequency of a local oscillator circuit, the 32768 Hz-frequency from an oscillator circuit for measuring time.
Further, in Patent Document 2, technology is disclosed that in addition to the configuration disclosed in Patent Document 1, includes a time measurement circuit and a frequency adjusting unit in the oscillator circuit, whereby the reference frequency output by the oscillator circuit is adjusted enabling the most stable oscillation of the local oscillator circuit.
Patent Document 1: Japanese Patent No. 3333255
Patent Document 2: Japanese Laid-Open Patent Publication No. 2004-294357